class_docstr: Teacher that will shift message['labels'][0] into message['text'] for whatever task
  is specified with --wrapper-task.
  
  Because the dialogue history is effectively overwritten by this action, all episodes
  will be flattened into one example each.
code: def __init__(self, opt: Opt, shared=None):
      super().__init__(opt, shared)
  
imports: from typing import Optional
  from parlai.core.params import ParlaiParser
  import copy
  from abc import ABC
  from parlai.core.agents import create_agent_from_shared
  from parlai.core.message import Message
  from parlai.core.opt import Opt
  from parlai.core.teachers import create_task_agent_from_taskname, FixedDialogTeacher, Teacher
  from parlai.utils.misc import warn_once
label_desc: Use image node_id 1 to create a new LabelToTextTeacher object from inherited base classes: AbstractWrapperTeacher with example: obj = LabelToTextTeacher(opt, shared)